Inconsistent Detection of Sites of Metastatic Non-Clear Cell Renal Cell Carcinoma with PSMA-Targeted [18F]DCFPyL PET/CT

PurposeTo investigate the utility of prostate-specific membrane antigen (PSMA)-targeted [F-18]DCFPyL positron emission tomography (PET)/X-ray computed tomography (CT) imaging for the detection of sites of disease in patients with metastatic non-clear cell renal cell carcinoma (RCC).ProceduresEight patients with metastatic non-clear cell RCC underwent imaging with PSMA-targeted [F-18]DCFPyL PET/CT. Imaged RCC histologic subtypes included papillary RCC (n=3), chromophobe RCC (n=2), unclassified RCC (n=2), and Xp11 translocation RCC (n=1). Using comparison to conventional CT and/or magnetic resonance imaging as reference, two radiologists with expertise in nuclear medicine identified putative sites of disease on [F-18]DCFPyL PET/CT and classified each lesion as having no radiotracer uptake, equivocal uptake, or definitive uptake.ResutsIn total, 73 metastatic sites and 3 primary tumors compatible with sites of non-clear cell RCC were identified on conventional imaging. Metastatic sites of disease included lymph nodes (n=40), venous thrombi (n=3), pulmonary nodules (n=10), bone lesions (n=15), brain lesions (n=3), and retroperitoneal masses (n=2). Only 10 of the 73 lesions (13.7%) were classified as having definitive radiotracer uptake (median SUVmax=3.25, range=1.2-9.5), 14 lesions (19.2%) had equivocal uptake (median SUVmax=2.85, range=0.5-6.5), and 49 lesions (67.1%) had no definitive uptake above background (median SUVmax=1.7, range=0.2-3.0). The three primary renal tumors demonstrated lower radiotracer avidity relative to surrounding normal renal parenchyma.ConclusionsA small proportion of sites of non-clear cell RCC showed uptake of the PSMA-targeted radiotracer [F-18]DCFPyL. Unlike for clear cell RCC, the results of this study indicate that PSMA-based PET is not appropriate for imaging other RCC subtypes.